Ease of Play
Players can count on her system mastery, and thus there's little argument when she makes a rule call during a session. This can make things go a lot faster when confusion or conflicts over rules arise (and they will. No matter how good the GM is, the systems were written and edited by non-ideal people). Knowing the system can help us adjudicate these calls, but we can leave room for debate after the session, or between sessions. If there's a clear answer which no one was able to cite at the time, then it can be looked up and remember for next time, and if it's a genuine conflict, then the original call (unless there are greater implications which weren't foreseen at the time) ought to stand, to keep things consistent.
The ideal GM uses her system mastery to coach the players. This is especially important during character creation with new players, where they can bring a concept to the table and the GM can help them use the mechanics to make it work. Even experienced players might have an idea and not know quite how to implement it, and we can help with that. I use the term coaching because it's not about helping them make the best character in the game, but the best character which fits their goals and criteria. We can do this by holding a few sessions for character creation where we sit down personally with players and help them realize their ideas. After all, we spend a lot more time with the rulebooks than the average player. Having a character which fits the picture in their head will help them have more fun, which helps us have more fun. It will also make the game more open to new players, and less intimidating.
As displayed above, system mastery helps cultivate trust. For the ideal GM, her players trust her implicitly within the context of the game. For us, that trust is the foundation of our credibility, that we know what we're talking about. And even if we drift away from the rules (which sometimes happens, usually for rule of cool), that trust reminds us why we stay close to them. The ideal GM doesn't talk about authority at all, she talks about her responsibility to the trust the players place in her, and part of what they trust is that she knows the rules.
So system mastery is definitely something the ideal GM has, and it's something we should aspire to, but what if it's a big system, we just don't have the time or inclination to read rulebook after rulebook, or one of the players just knows the rules better than us? An answer to the first two challenges is just to take your time. You shouldn't need to study, but as you have questions, look them up. Another is to become part of a community of people who also have system mastery. I know a lot of rpg forums have an Ask a Simple Question thread, and I've relied on them a lot. They can usually provide a text citation to back up their answers. And if there's a player at the table who's more familiar with the rules than us, we can use that. Defer to them and look it up later. That's an opportunity to educate ourselves and shows that we care about consistency with the rules rather than having our own way.
So that's system mastery, the first Ideal GM article. If you found it helpful, let me know. If you didn't., I'd loove to hear how I could make it more helpful, or if you have any thoughts on other ways we can use system mastery to make the game more fun. If you've got an idea for a topic, feel free to contact me by email (jtgwell [at] gmail [dot] com), or on Twitter (@ConceptCrucible)